Study On The Impact Of Climate Variability And Human Activities On The Shortage Of Blue/green Water Resources In The Xiangjiang River Basin Based On Swat Model

Due to human activities and frequent extreme climates,human beings face a shortage of fresh water resourc es.In regions with rapid economic development,it is extremely important to quantify the spatial distribution of water resources under the influence of climate change and human activities.In order to improve the effective use of water resources,studying on water resources management mainly focuses on blue and green water resources,which will help decision makers to manage water resources reasonably.Blue water resources are defined as free-flowing water in rivers,lakes,wetlands and underground aquifers.Blue water resources are mainly used for industrial production,agricultural irrigation,residents' lives and river ecological water.Green water resources are defined as water from which precipitation returns to the atmosphere through surface evapotranspiration and plant transpiration,and also includes water contained in the surface soil layer.Green water resources mainly maintain crop production,forestry and terrestr ial ecosystems.Therefore,studying on blue and green water resources plays a vital role in maintaining ecosystem stability and global food security.This paper took the Xiangjiang River Basin as the research area.Based on the future land use and climate scenarios,this paper established a SWAT model to quantify the amount of blue water and green water resources,analyzed the key factors affecting the shortage of blue water and green water resources,and identified the hot spots of water resources shortage in the basin.First,the blue and green water resource s were simulated by SWAT model.Combined with basic data such as the regional geographic elevation DEM of the Xiangjiang River Basin,the SWAT model was established.Then it was calibrated and validated according to the daily runoff data of five hydrological stations(Xiangtan station,Zhuzhou station,Hengshan station,Hengyang station and Guiyang station)in the main stream of Xiangjiang River.Then through the output of the SWAT model and the per capita comprehensive water consumption,the blue water and blue water scarcity,green water and green water scarcity were calculated respectively.The results showed that the monthly runoff of the five hydrological stations in the Xiangjiang River Basin achieved the expected results during the calibration period(2008-2012)and the validation period(2013-2017).When the coefficient of determination(R2)>0.6,Nash-Sutcliffe efficiency coefficients(NS)>0.5 and percent bias(BIAS)?±20%,the model simulation results were satisfactory.Next,qualitatively analyzing the impact of land use and climate change on blue and green water resources.The land use in 2050 was predicted by CA-Markov model,then the future climate data(2040-2060)was downscaled,and then these processed data were imported into the SWAT model for simulation to quantify the single and combined effects of future land use change and future climate change on blue and green water resources and their scarcity in Xiangjiang River Basin.The research results showed that the CA-Markov model integrates the functions of the CA model and the Markov model.The model results show ed that the Kappa value was 0.76,and the simulation results were satisfactory.The impacts of land use change and climate change on the spatiotemporal distribution of bl ue and green water resources were not simple synergistic effects.The spatiotemporal distri bution of blue water resources was mainly affected by the combination of urban land,agriculture land,forest land and precipitation.The spatiotemporal distrib ution of green water resources was mainly affected by the combination of urban land,agriculture land,precipitation and temperature.Finally,determining the key factors and hot spots that affect the blue and green water shortage.Based on redundancy analysis,this paper studied the relationship between 6 environmental(population,urban land,agricultural land,forest land,precipitation and temperature)factors and 49 cities/counties in different geographical locations,classified the sample data sets by cluster analysis to find out th e hot spots,and then determined the key factors affecting the shortage of blue and green water resources by correlation analysis.The research results showed that blue water scarcity was mainly affected by precipitation and population.It was positively correlated with precipitation(r = 0.425)and negatively correlated with population(r =-0.612).Green water scarcity was mainly affected by agricultural land and urban land.It was positively correlated with agricultural land(r = 0.429)and negatively correlated w ith urban land(r =-0.593).The hot spots for the shortage of blue water resources were mainly in Changsha,Xiangtan and Zhuzhou in the lo wer reach of the Xiangjiang River Basin.The hot spots for the short age of green water resources were mainly Changsha,Xiangtan and Zhuzhou in the lower reach of the Xiangjiang River basin;Shaodong and Hengyang in the middle reach;and Jianghua in the upp er reach.In the lower,middle and upper reaches of the Xiangjiang River Basin,the hotspot areas with the shortages of blue and green water resources accounted for 29.7%,4.6%,and 3.4%of the total area,respectively.As can be seen from the hotspot areas of the shortage of blue and green water resources in the Xiangjiang River Basin,there are serious shortages of blue and green water resources in Changsha,Xiangtan and Zhuzhou in the lowe r reaches of the basin.It is necessary to properly control the scale of urban expansion and improve the water supply network,so as to alleviate the pressure of water shortage.This study would provide useful information for water resources management in corresponding human-water system and would help regional watershed managers to make reasonable decisions on water resources management and protection in the Xiangjiang River Basin.